DEC = Decrease Register by 1
| Hex | Mnemonic | Cycles |
|---|---|---|
| 88 | DEC A | 8 |
| 89 | DEC B | 8 |
| 8A | DEC L | 8 |
| 8B | DEC H | 8 |
| 8C | DEC N | 8 |
| 8D nn | DEC [N+#nn] | 16 |
| 8E | DEC [HL] | 12 |
| 8F | DEC SP | 8 |
| 98 | DEC BA | 8 |
| 99 | DEC HL | 8 |
| 9A | DEC X | 8 |
| 9B | DEC Y | 8 |
Execute
A = (8-Bits) Register A
B = (8-Bits) Register B
L = (8-Bits) Register L
H = (8-Bits) Register H
N = (8-Bits) Register N
SP = (16-Bits) Register SP (Stack Pointer)
BA = (16-Bits) Register BA: (B shl 8) or A
HL = (16-Bits) Register HL: (H shl 8) or L
X = (16-Bits) Register X
Y = (16-Bits) Register Y
[N+#nn] = (8-Bits) Memory: (I shl 16) or (N shl 8) or #nn
[HL] = (8-Bits) Memory: (I shl 16) or HL
; DEC Ds
;
; Ds = Source/Destination
Ds = Ds - 1
Description
"Destination" is decremented by 1.
Conditions
Zero: Set when result is 0
Carry, Overflow and Sign remain unchanged
Examples
; A = 0x55
DEC A
; A = 0x54 (0x55 - 1 = 0x54)
; F = (Zero=0)
; [N+0x88] = 0xFF
DEC [N+$88]
; [N+0x88] = 0xFE (0xFF - 1 = 0xFE)
; F = (Zero=0)
; BA = 0x2997
DEC BA
; BA = 0x2996 (0x2997 - 1 = 0x2996)
; F = (Zero=0)
; X = 0xFFFF
DEC X
; X = 0xFFFE (0xFFFF - 1 = 0xFFFE)
; F = (Zero=0)